The present invention improves the structure of the three-dimensional homologous surveying instrument disclosed in U.S. Pat. No. 5,138,771, enabling the reading of a three-dimensional survey to be quickly read out.
Conventionally for testing the vertical of an object 72 (see FIG. 16), a pendulum 7 is suspended from a cord 71 and moved by hand, and then is released in order to determine and minimize the distance between the object 72 and the pendulum 7. However, it takes the pendulum time to come to a stand still and when it does, the handing line hardly ever gets close enough to the target to be acceptable without repeating the measurement, making the process troublesome and resulting in reading errors as well as time wasted and imprecision. FIGS. 17 and 18 show a surveying instrument according to the prior art. This structure of surveying instrument 8 comprises a base 81, and two glass tubes 82;83 positioned on the base 81 at right angles. The glass tubes 82;83 are marked with reference signs 822;832, and filled with liquid containing air bubbles 821;831, the air bubbles 821;831 seeking the highest point in the tubes 82;83 for horizontal surveying. However, due to the nature of liquid and low sensitivity of air bubbles, accurate precision can not be obtained. Th liquid used is easily affected by weather, which also causes enlargement of the air bubbles. The aforesaid and other known conventional surveying instruments are generally for one-dimension surveys, but they can not indicate the angles through three-dimensional rotation.